1. Field of the Invention
This invention pertains to the field of four stroke cycle gasoline engines and specifically the field of means of regulating the torque of such engines by delaying the time of intake valve closing so as to achieve an approximate Atkinson cycle at part load in lieu of the conventional Otto cycle, as achieved by the use of an intake throttle for torque regulation.
2. Description of the Prior Art
The essential prior art is presented in the earlier application cross referenced above. When a dashpot is used, as described therein, to adjustably delay intake valve closure the engine torque will rise at fixed torque control setting when engine speed decreases. This engine characteristic of rising torque with decreasing speed is desirable in certain engine uses as for example, in earthmoving or agricultural machinery. In other engine uses, as for example, passenger automobile drives, such an engine torque characteristic is undesirable. For passenger automobile engines a constant torque or only slightly rising torque with decreasing speed is preferred as being the engine torque characteristic to which passenger car drivers are accustomed.
The gasoline engine torque regulator, described in the earlier application cross referenced above, connects a piston and cylinder dashpot between the engine intake valve and the engine frame. This dashpot is fitted with a check valve flow passage which opens fully during valve opening to allow free flow of dashpot fluid between chambers when the engine intake valve is being opened by the intake cam and valve linkage. When the engine intake valve is being closed by the action of the intake valve spring the check valve closes and return flow of dashpot fluid then takes place via an adjustable restricted flow passage. In this way the closing of the engine intake valve may be adjustably delayed, by adjustment of the restriction in the restricted flow passage, beyond the usual intake valve closing time of at or near piston bottom dead center. As intake valve closing is longer delayed an increasing portion of the air-fuel mixture drawn into the engine cylinder during the intake stroke is pushed back into the intake manifold as the piston rises during the compression stroke. The amount of air-fuel mixture thusly returned to the intake manifold is proportional to the delay of intake valve closure beyond piston bottom dead center expressed in engine crankshaft degrees or, equivalently, expressed in percent of piston return stroke. Hence engine torque, which is proportional to the amount of air-fuel mixture left in the engine cylinder at intake valve closure, must decrease in proportion to the crankshaft degrees of delay of such valve closure. Since the dashpot devices of my earlier referenced invention delay intake valve closure by a fixed time interval, at any one setting of the flow restriction, engine torque must increase as engine speed decreases since the delay interval in crankshaft degrees is necessarily decreased thereby.